The present invention relates to lanthanide.sup.III complexes of 1,3-diketones, which complexes have a high luminescence quantum yield as well as long-lasting luminescence, a narrowband emission spectrum and bright triboluminescence. The invention also relates to the use of said compounds for optical sensors sensitive to impact, tension or pressure.
The phenomenon of triboluminescence (emission of light under strong mechanical stress) has long been known and is described, inter alia, in Advances in Physics 1977, Vol. 26, No. 6, 887-948 or in Math. Naturwiss. Unterricht 45/4, 1992, 195-202. A great number of crystalline compounds display this phenomenon, but as yet only very few are known whose emission is so strong as to be easily observable also in daylight. The brightest triboluminescent substance known so far is triethylammonium tetrakis(dibenzoylmethanato)europate(III).
Although the phenomenon of triboluminescence is well known, its cause cannot be completely accounted for yet and hence no predictions can be made concerning the occurrence of particularly intense triboluminescent compounds.
Specific Eu(III) complexes with pyridine-N-oxide, 2-, 3-, or 4-picoline-N-oxide and bipyridine-N,N-dioxide as well as thenoyltrifluoroacetone as ligand are disclosed in CA 114(18):177114p as triboluminescent substances of intense brightness.